Communication applications, such as industrial control applications, can be harsh environments for the transmission of communication signals within a communication network. This is in part due to the amount of electromagnetic noise within the environment. As such, communication protocols and transmission media through which the communication signals are transmitted often have to be robust so that they can withstand the potentially corrupting effects of electromagnetic interference. Communications which are robust to such noise typically require high transmission power and/or resilient signalling techniques. In addition, in some environments the distance covered by communication signals may be large, which provides further constraints upon the implementation of a communication network within an industrial control environment.
Industrial control environments typically implement communication networks, such as control networks, comprising a number of control modules which may act as nodes for the network. In some control networks, some nodes are displaced from others, whilst other nodes are grouped together in close proximity. Where some of the modules or nodes are located in close proximity, such as to take measurements or transmit control signals to a particular device or for other actions to take place, the relevant modules may also be mechanically coupled to one another. In an attempt to reduce the cost of implementing a control network, it is common to separate communications into sections which use different protocols. A first protocol may be used for communication over a long distance in an often noisy environment and a second, different, communication protocol used for communication between modules which are grouped together.
The second protocol may be a simpler or less robust protocol than the first protocol because it is operating in a relatively benign environment often between mechanically coupled modules. The second protocol may differ in that the packet structures and/or physical layer properties are not the same as the first protocol. As such, the displaced nodes within the control network may communicate using a first protocol and a group of nodes within the control network may separately communicate with one another using a second protocol. Such arrangements require protocol conversion circuitry to convert between the first protocol and the second protocol. The protocol conversion circuitry, however, is typically active circuitry which requires external electrical power and signal processing which increases the power requirements, cost and complexity of the control network implementation and may also add processing delays to the communication. This is particularly disadvantageous for industrial control environments which may require fast acting real time or deterministic communication.
What is needed is an implementation of communication within a control network in which the cost and complexity is reduced without negatively impacting upon the effectiveness of the network communication.